To support full-duplex, 2-way communication, many satellite communications applications require that a particular satellite link use a specific combination of frequency band and polarization for the transmit portion of the link and a different combination of frequency band and polarization for the receive portion of the link. Additionally, satellite communications applications may require that the polarizations for each distinct band be periodically changed or switched to support oppositely polarized satellite transponders, or to counteract (“track-out”) relative changes in polarization that may occur as a result of antenna orientation or geo-location. Earth station antennas used in airborne operations that operate in the Ka communications band, for instance, typically need to be capable of switching from Right Hand Circular polarization to Left Hand Circular polarization with little or no input from the operator.
A typical method for switching the circular polarization of a Ka-band antenna is to bring the circularly polarized transmit and receive signals to the back of the array, and then switch the polarization to the opposite sense using a polarization switch (which tends to be expensive and bulky). Another method of switching polarization is to physically “flip” a polarizer mounted on the face of the planar array antenna. However, a substantial increase in package volume is required to support such approach.
A common practice for altering the polarization of linear polarized reflector antennas is to physically rotate a dual linear polarized horn antenna that is used to feed such reflector antennas, rotating polarization in the process. However these types of antennas are bulky and exhibit poor efficiency when required to fit in limited volumes such as under radomes mounted on ground vehicles or aircraft. Planar antennas on the other hand, can be made with more extreme aspect ratios (length vs. height) to support such packaging challenges. A common practice of rotating the linear polarization of this type of antenna is achieved via the use of an Orthomode Transducer (OMT). In the case of circularly polarized antennas and some linear polarized antennas, a separate polarization switch is often employed to rotate one sense of circular to the other (e.g., left hand circular to right hand circular). Both approaches, however, have their drawbacks since OMT's and polarization switches tend to be large in size, heavy, expensive, and in many cases, suffer from high ohmic losses.
Another method of switching circular polarization (CP) is to physically “flip” a low-loss linear-to-CP polarizer mounted on the face of the planar array antenna. However, a substantial increase in package volume is required to support such an approach.